X-ray computed tomography or CT is a method of imaging the inside of the body using an x-ray beam. As the x-ray flux passes through the body, it is absorbed by bones, tissues, fluid, etc. within the body, thereby varying resultant flux intensity. The intensity of the x-ray flux emerging from the body is measured by detectors, and then the data are reconstructed into a detailed picture.
Multi-slice CT scanners are special CT systems equipped with a multiple-row detector array rather than a single-row detector array. This allows for simultaneous scan of multiple slices at adjacent locations.
A typical CT scanner includes a gantry having an annular frame for supporting an annular disk about a rotation or scanning axis of the scanner. The disk includes a central opening large enough to receive a patient extending along the scanning axis, and the disk is rotated about the patient during a scanning procedure. An x-ray tube is positioned on the disk diametrically across the central opening from an array of x-ray detectors. As the disk is rotated, the x-ray tube projects a flux of energy, or x-rays, along a scan plane, through the patient, and to the detector array. By rotating the x-ray source about the scanning axis and relative to the patient, x-rays are projected through the patient from many different directions. An image of the scanned portion of the patient is then reconstructed from data provided by the detector array using a computer.
In multi-slice CT reconstruction, it is a common practice that overlapping reconstruction is performed. That is, adjacent transverse slices have a significant overlap so that the inherent longitudinal image resolution can be utilized. Traditional methods for overlapping reconstruction are based on filtered back-projection, and are quite time-consuming and noise sensitive.
In CT fluoroscopy, CT images of a particular location or fixed volume are continuously generated to provide real time feedback to the CT operators. This currently requires a patient to be scanned continuously to update a complete dataset during the entire procedure. It is desirable, however, to be able to produce updated images with projections less than the complete dataset.
In bolus chasing for CT angiographic studies, a set of preparatory scans is acquired at a particular location to monitor the arrival of a contrast agent. When the contrast level reaches a pre-determined threshold, helical scans are initiated. If partial projections can be used to produce images, a significant dose minimization will result from the preparatory scans.
A disadvantage of the aforementioned current systems is that the reconstruction algorithms essentially rely on complete projection datasets to produce an image (180° for parallel flux and 180 plus a fan angle for fan beam flux). Images reconstructed with these algorithms require higher x-ray dose and are subject to degraded temporal resolution and increased noise.
The disadvantages associated with current CT systems have made it apparent that a new technique for CT scanning and image reconstruction is needed. The new technique should substantially increase information acquired from each patient while minimizing the required amount of data or scan dose. The present invention is directed to these ends.